1. Field of the Invention
The present invention relates to a torque transmission device in which two shafts (rotary shafts) are coaxially connected to transmit torque.
2. Description of Related Art
JP-A-2004-320842 discloses an electric power steering device in which a shaft center of a worm shaft of a decelerator is matched with a shaft center of a motor shaft of a motor to thus reduce vibration and noise while realizing size-reduction of the device. In this device, individual bearings are respectively provided to both tip ends of each of two rotary shafts, i.e., the motor shaft and the worm shaft, and each of the two rotary shafts is supported by the two bearings, respectively. A relative movement of both rotary shafts in an approaching direction is regulated by abutment between the bearing at a connection end of each rotary shaft and a step surface of each rotary shaft. In this support structure, opposing shaft ends of both rotary shafts are directly spline-connected, and torque is transmitted from the motor shaft to the worm shaft via the spline connecting part.
However, according to the structure disclosed in JP-A-2004-320842, when a shaft deviation and the like occur, stress is caused at the spline connecting part. Also, since the connection ends of both rotary shafts are supported by the individual bearings, the stress is apt to increase. Also, the stress occurring at the abutting part which regulates the relative movement of both rotary shafts in an approaching direction may be also increased due to a relatively short distance between the abutting part and the spline connecting part.